1. Field of the Invention
The present invention relates to a power generation device that generates energy (converting energy from kinetic energy (energy of vibration) to electrical energy) by varying the distance between a dielectric body and an electret; and in particular to a capacitive power generation device of vibratory drive design, manufactured employing a micro electromechanical system (MEMS) technique.
2. Description of Related Art
FIG. 33 is a schematic diagram showing a prior art example of a vibratory power generation device. In FIG. 33, reference numeral 101 designates an upper substrate, reference numeral 102 designates a lower substrate, reference numeral 103 designates an electret, reference numeral 104 designates an opposite electrode, reference numeral 105 designates a base electrode, and reference numeral designates 106 a spring. The upper substrate 101 is a moveable body that is elastically supported so as to be displaceable in two axial planar directions (an X direction and a Y direction) with respect to the lower substrate 102.
The basic principle of operation of a vibratory power generation device having the aforementioned configuration is a system whereby the surface area of overlap of the electret 103 and the opposite electrode 104 is varied through vibration in two axial planar directions (the X direction and the Y direction) while maintaining a predetermined gap distance, to extract, in the form of electrical current, changes in electric charge induced in the opposite electrode 104 (a so-called electrostatic induction system).
As techniques related to vibratory power generation devices manufactured employing MEMS techniques, there may be cited Patent Document 1 (Japanese Laid-Open Patent Application 2007-312551); Non-patent Document 1 (Y. Naruse, N. Matsubara, K. Mabuchi, M. Izumi, K. Honma, “ELECTROSTATIC MICRO POWER GENERATOR FROM LOW FREQUENCY VIBRATION SUCH AS HUMAN MOTION”, Proceedings of PowerMEMS 2008+, Sendai, Japan, Nov. 9-12, (2008); and Non-patent Document 2 (M. Edamoto, Y. Suzuki, N. Kasagi, K. Kashiwagi, Y. Morizawa, T. Yokoyama, T. Seki, and M. Oba, “LOW-RESONANT-FREQUENCY MICRO ELECTRET GENERATOR FOR ENERGY HARVESTING APPLICATION”, Proc. IEEE Int. Conf. MEMS 2009, Sorrento, (2009), pp. 1059-1062.
However, in the aforementioned vibratory power generation device of the prior art, the generated power is at most on a microwatt scale, and applications for it were limited.
Moreover, the aforementioned vibratory power generation device of the prior art has a structure in which the electret 103 and the opposite electrode 104 are facing one another, and when the gap distance between the electret 103 and the opposite electrode 104 is designed too small, electrostatic attraction acting between the electret 103 and the opposite electrode 104 poses a risk of the two coming into contact, or of the charge introduced from the electret 103 being discharged. For this reason, the gap distance between the electret 103 and the opposite electrode 104 must be designed to be somewhat large, but having thusly expanded the gap distance, it now becomes necessary to design the electret 103 and the opposite electrode 104 to have large surface areas, in order for vibration-induced change in capacity to be large, giving rise as a result to a negative cycle whereby the gap distance must be expanded even further. Due to this sort of negative cycle, in the aforementioned vibratory power generation device of the prior art, it has been difficult to miniaturize the device and/or reduce the gap size, while boosting the generated power.